The present invention relates generally to semiconductor packaging using surface-mount technologies (SMTs), and, more particularly, to mold tooling used in assembling semiconductor packages.
In the field of semiconductor packaging, there has been a demand for smaller packages yet with an increased number of leads. The number of leads has typically been limited by factors such as the size of the package and the pitch of the leads. Decreasing the spacing between leads increases the likelihood that the leads will be shorted together.
In order to overcome these problems, packaged semiconductor devices have been developed that have two sets of metal leads, where the first set of leads begins on a first plane and the second set begins on a second plane, different from the first plane. Such packaged semiconductor devices are capable of having greater numbers of leads than comparable packaged semiconductor devices in which all of the metal leads begin on the same plane.
FIGS. 1A and 1B show cross-sectional and side views, respectively, of a conventional packaged semiconductor device 100 having sets of metal leads that begin on two different planes. The following discussion provides a brief explanation of the device 100 and a method for bending the leads and encapsulating the device 100 in molding compound.
The device 100 has a metal lead frame 102 comprising a die paddle 104 and first and second sets of leads 106 and 112. The die paddle 104 is positioned on a first horizontal plane H1 of the device 100. The leads 106 and 112 are physically and electrically isolated from each other and from the die paddle 104. Each of the leads 106 has (i) a proximal end 108 that is located on the same horizontal plane H1 as the die paddle 104 and (ii) a distal end 110 that extends away from the die paddle 104 to a second horizontal plane H2. Each of the leads 112 in the second set of metal leads has (i) a proximal end 114 that is located on a third horizontal plane H3 that is above the first horizontal plane H1 and (ii) a distal end 116 that extends away from the die paddle 104 to the second horizontal plane H2.
In addition, each lead 112 is bent toward the bottom of the device 100 such that the lead 112 clears the distal end 110 of the adjacent leads 106. In this embodiment, two leads 106 and three leads 112 are shown in FIG. 1B on the front side of the device 100. However, the numbers of the leads 106 and 112 may be greater than that shown, and the spacing between the leads 106 and 112 may be smaller than that shown.
As shown in FIG. 1A, at least one integrated circuit (IC) die 118 is mounted on the die paddle 104. Further, bond wires 120 electrically connect (i) die pads (not explicitly depicted) on the upper surface (i.e., active side) of the IC die 118 and (ii) the proximal ends 108 and 114 of the leads 106 and 112, respectively. The die paddle 104, the IC die 118, the proximal ends 108 and 114 of the leads 106 and 112, respectively, and the bond wires 120 are encapsulated in a molding compound 122, which protects these components from contamination and damage.
FIGS. 2A and 2B show side views that illustrate steps of encapsulating the packaged semiconductor device 100 of FIGS. 1A and 1B in the molding compound 122 using a mold 200.
In FIG. 2A, a partially-assembled packaged semiconductor device comprising the lead frame 102, IC die 118, and bond wires 120 is positioned between upper and lower halves 202 and 212 of a mold 200. Before molding, the lead frame 102 is a planar piece of metal having the die paddle 104 and the leads 106 and 112 formed thereon for example by etching, cutting, and/or stamping. Note that the distal ends 110 and 116 of the metal leads 106 and 112, respectively, are connected to one another by connecting bars 124, which are cut away after the molding process. However, for illustrative purposes, the connecting bar 124 that interconnects the leads 106 and 112 projecting out of the package 100 is not shown in FIG. 2A or 2B.
The upper mold half 202 comprises a plurality of chamfered teeth 204 and a space 208 located on either side of each tooth 204. Further, the upper mold half 202 has an upper mold cavity 210 formed therein. The upper mold cavity 210 is not visible in the side view, and therefore, it is shown via dashed lines to indicate that it is hidden from view.
Similarly, the lower mold half 212 comprises a plurality of chamfered teeth 214, a space 218 located on either side of each tooth 214, and a lower mold cavity 220. The teeth 214 and spaces 218 of the lower mold half 212 alternate with the teeth 204 and spaces 208 of the upper mold half 202 such that (i) the teeth 204 of the upper mold half 202 mate with the spaces 218 of the lower mold half 212 and (ii) the teeth 214 of the lower mold half 212 mate with the spaces 208 of the upper mold half 202. Note that all four sides of the mold 200 may be similar in appearance to the side shown in FIG. 2A.
In FIG. 2B, the mold 200 is in a closed position with the partially-assembled packaged semiconductor device positioned therein. As shown, when the upper and lower mold halves 202 and 212 are brought together, the leads 106 are bent into the spaces 218 of the lower mold half 212 in alignment with horizontal plane H1 by the teeth 204 of the upper mold half 202, and the leads 112 are bent into the spaces 208 of the upper mold half 202 in alignment with horizontal plane H3 by the teeth 214 of the lower mold half 212. Chamfers 206a and 206b (FIG. 2A) are formed on the teeth 204, and chamfers 216a and 216b (FIG. 2A) are formed on the teeth 214 to help guide the teeth 204 and 214 into the corresponding spaces 218 and 208, respectively, on the opposing mold half.
After the mold 200 is closed, the molding compound (not shown) is injected into the cavities 210 and 220 of the mold 200. When the molding compound cures, the metal leads 106 and 112 are held in place on the two horizontal planes H1 and H3 by the cured molding compound. It would be advantageous to be able to form a package having leads that lie in spaced parallel planes but with reduced resin bleeding and where the dimensions of the leads and the lead pitch is reduced.